Ostrich eggshell bead diameter in the Holocene: Regional variation with the spread of herding in eastern and southern Africa

Abstract

Despite their ubiquity in Holocene African archaeological assemblages, ostrich eggshell (OES) beads are rarely studied in detail. An exception is in southern Africa, where there is a proposed relationship between OES bead diameter and the arrival of herding ~2000 years before present. In 1987, Leon Jacobson first observed that beads from forager sites in Namibia tended to be smaller than those associated with herder sites. Studies examining bead size around the Western Cape have generally confirmed Jacobson's findings, though the driving forces of the diameter change remain unknown. Since this time, diameter has become an informal way of distinguishing forager and herder assemblages in southern Africa, but no large-scale studies of OES bead variation have been undertaken. Here we present an expanded analysis of Holocene OES bead diameters from southern, and for the first time, eastern Africa. Results reveal distinct patterns in OES bead size over time, reflecting different local dynamics associated with the spread of herding. In southern Africa, OES diameters display low variability and smaller absolute size through time. While larger beads begin to appear <2000 years ago, most beads in our study remained smaller. In contrast, eastern African OES bead diameters are consistently larger over the last 10,000 years and show no appreciable size change with the introduction of herding. Notably, larger beads thought to be associated with herders in southern Africa fall within the range of eastern African beads, indicating a potential connection between these regions in the Late Holocene consistent with genetic findings. Regional differences in bead size are subtle, on the order of millimeters, yet offer a potentially important line of evidence for investigating the spread of herding in sub-Saharan Africa. In order to understand the meaning of these changes, we encourage additional studies of OES bead assemblages and urge researchers to report individual bead diameters, rather than averages by level.

Fig 1. Previously published OES bead diameter data for southern Africa.

Produced using data from [–,,–76].

Fig 2. Map of sub-Saharan Africa showing locations of sites used in this study.

New data shown with white squares, previously published data with black circles; basemap courtesy of Natural Earth (naturalearthdata.com).

Fig 3. OES bead diameters from southern Africa.

New data shown in green, previously published data in black.[83,84].

Fig 4. OES bead diameters from southern and eastern Africa.

Southern data shown in green, eastern data in blue. One eastern African outlier (14.49 mm) is not shown.

Fig 5. Scatter plots of OES bead diameters from southern and eastern Africa.

New southern data shown in green, new eastern data in blue, previously published data in black. Grey bars represent the introduction of herding into each region. Two eastern African outliers (14.49 and 10.07 mm) are not shown.

Fig 6. Examples of OES beads showing subtle size differences between regions.

Scale bar = 5 mm; (a) Nelson Bay Cave, South Africa; (b) Wonderwerk Cave, South Africa; (c) Magubike Rockshelter, Tanzania; (d) Daumboy 3 Rockshelter, Tanzania.